The optical fiber access network is the inevitable trend of optical fiber communication. The optical fiber access network normally has five sorts of topological structures as follows: single star topology, multi-star topology, tree topology, bus topology and ring topology. The former four sorts can be called star structure. Compared with ring network and point to point system, the star network can save more optical fibers and optical receiving and sending modules, and the branch structure of it is easy for coverage. Therefore, the star structure is normally adopted in the optical fiber access network.
For protecting the normal work of communication service, the optical fiber line needs to be protected in the optical fiber access network. In prior art, the protection manner of the optical fiber line between the optical line terminal and the optical network unit is as follows:
1. The manner of separate fiber in one cable is adopted for protection, i.e. a main optical fiber and a backup optical fiber are set in one optical cable. When the main optical fiber is cut off, the backup optical fiber can be used. However, when the whole optical cable is cut off, the normal operation of communication service can't be insured.
2. The manner of separate cable in one pipe is adopted for protection, i.e. the main optical fiber and the backup optical fiber are set in different optical cables in one pipe or routing so that when the main optical fiber is cut off at the optical cable, the backup optical fiber can be used. However, this manner can only be used to prevent the optical cable from ordinary failure of being cut off but not the heavy failure, for example, the accidence of extensive optical cable pipe being cut off because of the construction of large-scale machinery.
3. The manner of separate cable in separate pipes is adopted for protection, i.e. the main optical fiber and the backup optical fiber are not only in different cables but also in different pipes or routings. This manner provides the maximum protection to the optical fiber line, but the economic cost is very high.
Due to being restricted by pipe, optical fiber resources and the cost of construction, the optical fiber line between the optical line terminal and the optical branching divider is normally protected only by the above-mentioned manners, and the optical fiber line between the optical branching divider and the optical network unit is seldom protected in the star structure access network. Once the optical fiber has the failure of being cut off, the network communication will become invalid.
Although the users who is sensitive to the price and needs the real-time information communication don't have strict requirement to the QOS of network and can put up with temporary bad performance of the network, such as network speed declining and so on, they can't put up with the break down of the network for long time. Thus, the adoption of suitable and effective methods for the protection of the optical fiber access network is the necessary assurance for communication fluency of the user network.